The present invention relates to magnetic disc apparatuses used for information memory, and particularly relates to a specific type of magnetic disc apparatus designed to maintain an optimum humidity in a head disc assembly.
Conventionally, this type of magnetic disc apparatus generally utilizes a contact-start-stop (C.S.S.) drive. This drive is carried out such that a head for recording and reproducing information contacts a disc medium when it is stationary, and the head floats over the medium through an air film (air bearing) due to an air flow being generated during the rotation of the disc medium so as to effect recording and reproducing. In this drive, the head surface and the medium surface must be maintained flat precisely in order to improve the floating performance of the head and to avoid head clash.
However, when the head disc assembly (hereinafter, H.D.A.) contains air having relatively high humidity, the head tends to cling (i.e., adhere) to the medium when the head surface is placed in contact with the medium surface. This phenomenon has been reported in Japan Lubrication Society, the 33rd Spring Research Conference Brief, 1989, Andou and Miyamoto, "Affect of humidity to frictional characteristic of magnetic disc and slider." For this reason, conventionally desiccant is disposed inside the H.D.A. to remove moisture within the H.D.A. to prevent clinging.
Recently, intensive study has been reported about the relation between the generation of wearing and damage of the medium and the internal humidity of the H.D.A. in various papers such as Japan Lubrication Society, the 33rd Spring Conference Brief, 1989, Kouzu and Yamaguchi, "Influence of testing circumstance on lifetime of magnetic disc", and Japan Lubrication Society, the 34th National Conference, Toyama, Brief, 1989, Katsuno, Ueda and Tanaka, "Wearing and damage of magnetic disc (5)." According to these reports, the interior of the H.D.A. should be preferably maintained at a relatively high humidity in order to suppress wearing and damage of the medium. Namely, an excessively dry condition may cause wearing and damage of the medium.
In the above-noted conventional magnetic disc apparatus, while the interior of the H.D.A. is controlled at an optimum humidity degree during a stationary state to avoid clinging, the interior temperature rises during an operating state so that the relative interior humidity degree decreases to cause wearing and damage of the medium.
Further, when the H.D.A. stops operation, a contact stop is effected while the interior temperature increases and therefore the relative humidity degree is held at a low level. Namely, in the conventional magnetic disc apparatus, the head is made in contact with the medium in quite a low degree of relative humidity, thereby disadvantageously causing wear and damage.
This phenomenon is qualitatively described hereinbelow with reference to FIG. 4. FIG. 4 shows a change in the degree of relative humidity in a sealed air space in terms of temperature. This sealed situation simulates an enclosed H.D.A. having no desiccant and no intake opening. According to the graph. of FIG. 4, 40% RH of air at a room temperature of 25.degree. C. is changed to 7.5% RH of quite dry air at the operating temperature of the H.D.A., for example, 55.degree. C. Moreover, 60% RH air at the room temperature may be changed to less than 13% RH of air at the operating temperature to produce a considerably dry state. Besides, this air may develop water dew (e.g., moisture) at 15.degree. C., and therefore cannot be used practically. In order to avoid development of water dew, the relative humidity must be set below 20% RH. However, this condition becomes an excessively dry state of less than 5% RH at the operating temperature to cause a dangerous condition. The practical H.D.A. device is actually provided with a breathing filter communicating with the atmosphere, and a desiccant. However, the breathing filter has a moderate flow rate capacity so as to regulate a pressure difference between the interior and the exterior of the closed H.D.A. Hence, it is not sufficient to instantly remove the outstanding dry condition. The desiccant adversely works to develop this dry condition.